In an environment including narrowband jammers, substantial reduction of the effect of the jammer is enabled by utilising bandspreading. In principle the jammer may be of two kinds: (a) known jammers such as local TV stations, the frequency bands of which are known, and can therefore be avoided from the begining of communication, and (b) jammers operating at known or unknown frequencies or frequency bands during communication and are the most difficult to avoid.
The jammers according to (b) are those most difficult to avoid.
Radio communication using frequency hopping to provide bandspreading is already known in the art, as shown, for example, in EP-A1-0068690. In this known system, each signal received is analysed as to its quality. If more than one radio connection (transceiver) has hopped to the same frequency, no new signal is sent on the frequency of the received signal, but the frequency of a signal received earlier or later is used instead. Colliding frequencies are thus taken into consideration in this known system, but the frequency hop takes place solely through the selection of the frequency by random number generation.
In a conventional frequency hopping system, a new frequency f.sub.n is generated by a random number r.sub.n is created and used as an argument in a function H(r.sub.n), i.e. F.sub.n =H(r.sub.n). The selection of the frequency F.sub.r in a related receiver and transmitter should give the same values in the transmitter and receiver that are to communicate.